Dear Marcos, the systems Eliseo is working on are molecular magnets, they usually have well localized spins on 3d ions and can be brought to self-consistency in a number of different magnetic configurations. Even if (usually) there is a certain (single-determinant) ground-state magnetic configuration, it is Eliseo's good right to expect a number of other metastable states to converge as well. The exact numbers (from integrated charge density or Mulliken analysis) are usually unimportant, because they reveal in one or other way a certain arrangement of integer spins of 3d ions. And of course the fixed spin moment, if imposed, remains fixed at each iteration (at the expense of introducing two Fermi levels, also in each iteration).
Best regards Andrei +-- Dr. Andrei Postnikov ---- Tel. +33-387315873 ----- mobile +33-666784053 ---+ | Paul Verlaine University - Institute de Physique Electronique et Chimie, | | Laboratoire de Physique des Milieux Denses, 1 Bd Arago, F-57078 Metz, France | +-- [EMAIL PROTECTED] ------ http://www.home.uni-osnabrueck.de/apostnik/ --+ On Wed, 28 Nov 2007, Marcos Verissimo Alves wrote: | Eliseo, | | The numbers you are showing for the spins are extracted from some | integration over the densities, or those are the mulliken charges on the | system? I will suppose that those are the numbers that come out after one | or more complete self-consistency cycles; if it is so, it means that your | system "doesn't want to keep" the initial values you have supplied; it | will be more advantageous, energetically, to have the final configuration | of spins. The initial configuration is just a starting guess, but | self-consistency takes over after this. Nothing guarantees that you will | have the final global net spin, or the individual net spins of the atoms, | equal to the initial values after a whole SCF cycle. Actually, you can | constrain the total magnetization of a system in siesta, but I am not sure | if the total magnetization would be constrained over all the scf steps. | | Cheers, | | Marcos | | | | Vous avez écrit / You have written / Lei ha scritto / Você escreveu... | Eliseo Ruiz | > Dear Colleagues, | > | > I am calculating a periodic system with 40 Cu(II) cations in the | > unit cell. I am trying to | > calculate the energy for the different spin distributions. However, | > only in a couple of | > cases I obtain the signs of the spins that I specified in the input | > file. For instance, for one | > of the spin distributions: | > | > ............ | > # Spin defintion | > SpinPolarized T | > FixSpin T | > TotalSpin 8.0 | > %block DM.InitSpin | > 1 +1.0 | > 2 -1.0 | > 3 -1.0 | > 4 +1.0 | > 5 +1.0 | > 6 +1.0 | > 7 -1.0 | > 8 -1.0 | > 9 +1.0 | > 10 +1.0 | > 11 +1.0 | > ............ | > 40 +1.0 | > %endblock DM.InitSpin | > | > the results for the spin density: | > atom up down total | > 1 4.968 -5.401 -.433 | > 2 4.978 -5.411 -.433 | > 3 5.397 -4.948 .449 | > 4 5.406 -4.942 .464 | > 5 5.431 -4.963 .468 | > 6 5.407 -4.962 .445 | > 7 5.415 -4.977 .438 | > 8 4.957 -5.391 -.434 | > 9 4.943 -5.404 -.461 | > 10 5.439 -4.964 .475 | > 12 5.420 -4.987 .433 | > ............ | > | > The total spin is satisfied but not the local spins. I tried several | > options of DM.MixingWeight and | > DM.NumberPulay as well as for ElectronicTemperature but I cannot | > reach the selected spin | > distribution. | > | > best wishes, | > | > Eliseo | > | | | -- | Dr. Marcos Verissimo Alves | Post-Doctoral Fellow | Unité de Physico-Chimie et de Physique des Matériaux (PCPM) | Université Catholique de Louvain | 1 Place Croix du Sud, B-1348 | Louvain-la-Neuve | Belgique | | ------ | | Gort, Klaatu barada nikto. Klaatu barada nikto. Klaatu barada nikto. | |
